The budding popularity of solar panel and battery systems, driven by a drop in lithium-ion battery prices, has thrown a lifeline to Germany's solar sector. But many German solar firms have gotten back on their feet thanks to home energy storage systems. In just a few short years, home storage units morphed from a quirky niche product for tech nerds and Green Party voters to one with enormous mainstream potential. The consulting firm McKinsey predicts that the cost of energy storage systems will fall 50 to 70 percent globally by 2025 "as a result of design advances, economies of scale, and streamlined processes."